Deep trench semiconductor structure and method

ABSTRACT

An electrical structure and method of forming. The electrical structure includes a semiconductor substrate comprising a deep trench, an oxide liner layer is formed over an exterior surface of the deep trench, and a field effect transistor (FET) formed within the semiconductor substrate. The first FET includes a source structure, a drain structure, and a gate structure. The gate structure includes a gate contact connected to a polysilicon fill structure. The polysilicon fill structure is formed over the oxide liner layer and within the deep trench. The polysilicon fill structure is configured to flow current laterally across the polysilicon fill structure such that the current will flow parallel to a top surface of the semiconductor substrate.

FIELD OF THE INVENTION

The present invention relates to a field effect transistor comprising a gate structure formed in a deep trench.

BACKGROUND OF THE INVENTION

Structures formed on a substrate typically do not comprise the ability to isolate the structures from additional structures on the substrate. Accordingly, there exists a need in the art to overcome at least one of the deficiencies and limitations described herein above.

SUMMARY OF THE INVENTION

The present invention provides an electrical structure comprising:

a semiconductor substrate comprising a deep trench;

an oxide liner layer formed over an exterior surface of said deep trench; and

a first field effect transistor (FET) formed within said semiconductor substrate, wherein said first FET comprises a first source structure, a first drain structure, and a first gate structure, wherein said first gate structure comprises a first gate contact connected to a first polysilicon fill structure, wherein said first polysilicon fill structure is formed over said oxide liner layer and within said deep trench, wherein said first polysilicon fill structure is configured to flow current laterally across said first polysilicon fill structure such that said current will flow parallel to a top surface of said semiconductor substrate.

The present invention provides a method for forming an electrical structure comprising:

providing a semiconductor substrate;

forming a deep trench structure within said semiconductor substrate;

forming an oxide liner layer over an exterior surface of said deep trench; and

forming a first field effect transistor (FET) within said semiconductor substrate, wherein said first FET comprises a first source structure, a first drain structure, and a first gate structure, wherein said first gate structure comprises a first gate contact connected to a first polysilicon fill structure, wherein said first polysilicon fill structure is formed over said oxide liner layer and within said deep trench, wherein said first polysilicon fill structure is configured to flow current laterally across said first polysilicon fill structure such that said current will flow parallel to a top surface of said semiconductor substrate.

The present invention advantageously provides a simple structure and associated method for isolating structures from additional structures on a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a top view of an electrical structure, in accordance with embodiments of the present invention.

FIG. 1B illustrates a cross sectional view of the electrical structure of FIG. 1A, in accordance with embodiments of the present invention.

FIG. 2A depicts a first alternative to FIG. 1A, in accordance with embodiments of the present invention

FIG. 2B illustrates a cross sectional view of the electrical structure of FIG. 2A, in accordance with embodiments of the present invention.

FIG. 3A depicts a second alternative to FIG. 1A, in accordance with embodiments of the present invention.

FIG. 3B illustrates a cross sectional view of the electrical structure of FIG. 3A, in accordance with embodiments of the present invention.

FIG. 4 depicts a first alternative to FIG. 3A, in accordance with embodiments of the present invention

FIG. 5 depicts a first alternative to FIG. 4, in accordance with embodiments of the present invention

FIG. 6A depicts a third alternative to FIG. 1A, in accordance with embodiments of the present invention.

FIG. 6B illustrates a cross sectional view of the electrical structure of FIG. 6A, in accordance with embodiments of the present invention.

FIG. 7A depicts a first alternative to FIG. 6A, in accordance with embodiments of the present invention.

FIG. 7B illustrates a cross sectional view of the electrical structure of FIG. 7A, in accordance with embodiments of the present invention.

FIG. 8A depicts a combination FIGS. 2A and 3A, in accordance with embodiments of the present invention.

FIG. 8B illustrates a cross sectional view of the electrical structure of FIG. 8A, in accordance with embodiments of the present invention.

FIGS. 9A-4H illustrate a process for generating the electrical structure of FIGS. 8A and 8B, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a top view of an electrical structure 4 a, in accordance with embodiments of the present invention. Electrical structure 4 a may be any type of electrical structure that comprises electrical circuits including, inter alia, a semiconductor chip. Electrical structure 4 a comprises a field effect transistor (FET) 17 formed on a semiconductor substrate 23 (i.e., see FIG. 2). Semiconductor substrate 23 comprises a P substrate 24 and a silicon layer 22 (i.e., N-tub layer) formed from a portion of P substrate. An N-tub layer comprises a highly graded junction layer diffused to provide high voltage isolation. FET 17 comprises a P+ source structure 6 formed over a P-tub 18 a, a P+drain structure 7 formed over a P-tub 18 b, a gate dielectric (e.g., oxide) liner 16, a gate structure 14 formed over gate dielectric liner 16, and a gate contact 12 connected to gate structure 14. Source structure 6 may comprise a silicide contact layer 30 a. Drain structure 7 may comprise a silicide contact layer 30 c. Gate contact 12 may comprise a silicide contact layer 30 b. Gate dielectric (e.g., oxide) liner 16 may comprise a thickness of about 3000 A. P-tub 18 a and P-tub 18 b are formed from implants formed within silicon layer 22 (i.e., N-tub layer). A P-tub comprises a highly graded junction layer diffused to provide high voltage isolation. Gate dielectric liner 16 is formed within a deep trench 21 formed within P-tub 18 a, P-tub 18 b, and silicon layer 22 (i.e., N-tub layer). Gate structure 14 comprises a poly-silicon fill structure. Gate structure 14 is formed over gate dielectric (e.g., oxide) liner 16 and within deep trench 21. A deep trench is defined herein as a trench formed within a substrate (e.g., semiconductor substrate 23) that comprises a depth of at least 6 um. Gate structure 14 is configured to flow current laterally (i.e., in a direction 10) across gate structure 14 such that the current will flow parallel to a top surface 23 a of semiconductor substrate 23. FET 17 is a high voltage FET configured to operate at voltages selected from a range of about 10 volts to about 200 volts.

FIG. 1B illustrates a cross sectional view of electrical structure 2 a of FIG. 1A, in accordance with embodiments of the present invention. The cross sectional view of FIG. 1B is taken along line 1B-1B of FIG. 1A. The cross sectional view in FIG. 2 illustrates the depth D1 of deep trench 21 comprising gate structure 14 is formed over gate dielectric (e.g., oxide) liner 16. Additionally, the cross sectional view in FIG. 2 illustrates a shallow trench isolation (STI) structure formed over P-tub 18 a, P-tub 18 b, and gate structure 14 and surrounding source structure 6, drain structure 7, and gate contact 12.

FIG. 2A depicts a first alternative to FIG. 1A illustrating a top view of an electrical structure 4 b, in accordance with embodiments of the present invention. In contrast with electrical structure 4 a FIG. 1A, electrical structure 4 b of FIG. 2A comprises an FET 17 a that comprises a P-well 25 a formed between P-tub 18 a and source structure 6 and a P-well 25 b formed between P-tub 18 b and drain structure 7. A P-well is defined herein as a moderately P doped CMOS device.

FIG. 2B illustrates a cross sectional view of electrical structure 4 b of FIG. 2A, in accordance with embodiments of the present invention. The cross sectional view of FIG. 2B is taken along line 2B-2B of FIG. 2A.

FIG. 3A depicts a second alternative to FIG. 1A illustrating a top view of an electrical structure 4 c, in accordance with embodiments of the present invention. In contrast with electrical structure 4 a FIG. 1A, electrical structure 4 c of FIG. 3A comprises a deep trench 21 a forming a perimeter surrounding FET 17 a. A gate dielectric (e.g., oxide) liner 16 a is formed within (i.e., lining) deep trench 21 a and a gate structure 14 a is formed over gate dielectric liner 16 a and within trench 21 a. Deep trench 21 a, gate dielectric (e.g., oxide) liner 16 a, and gate structure 14 a in combination form a perimeter structure that surrounds FET 17 a. The perimeter structure formed by deep trench 21 a, gate dielectric (e.g., oxide) liner 16 a, and gate structure 14 a isolates (i.e., electrically and mechanically) FET 17 a from additional components (e.g., FETS, resistors, capacitors, wires, etc) that are located on electrical structure 4 c. Gate dielectric (e.g., oxide) liner 16 a may comprise a thickness of about 3000 A.

FIG. 3B illustrates a cross sectional view of electrical structure 4 c of FIG. 3A, in accordance with embodiments of the present invention. The cross sectional view of FIG. 3B is taken along line 3B-3B of FIG. 3A.

FIG. 4 depicts a first alternative to FIG. 3A illustrating a top view of an electrical structure 4 d, in accordance with embodiments of the present invention. In contrast with electrical structure 4 c FIG. 3A, electrical structure 4 d of FIG. 4 comprises a deep trench 21 b forming a perimeter surrounding FET 17 b and FET 17 c. Additionally, deep trench 21 b is formed between FET 17 b and FET 17 c. A gate dielectric (e.g., oxide) liner 16 b is formed within (i.e., lining) deep trench 21 b and a gate structure 14 b is formed over gate dielectric liner 16 b and within trench 21 b. Deep trench 21 b, gate dielectric (e.g., oxide) liner 16 b, and gate structure 14 b in combination form a perimeter structure that surrounds FET 17 b and FET 17 c. Additionally, deep trench 21 b, gate dielectric (e.g., oxide) liner 16 b, and gate structure 14 b in combination form an isolation structure that separates FET 17 b from FET 17 c. The structure formed by deep trench 21 b, gate dielectric (e.g., oxide) liner 16 b, and gate structure 14 b isolates (i.e., electrically and mechanically) FET 17 b from FET 17 c. Additionally, the structure formed by deep trench 21 b, gate dielectric (e.g., oxide) liner 16 b, and gate structure 14 b isolates (i.e., electrically and mechanically) FET 17 b and FET 17 c from additional components (e.g., FETS, resistors, capacitors, wires, etc) that are located on electrical structure 4 d. Gate dielectric (e.g., oxide) liner 16 b may comprise a thickness of about 3000 A.

FIG. 5 depicts a first alternative to FIG. 4 illustrating a top view of an electrical structure 4 e, in accordance with embodiments of the present invention. In contrast with electrical structure 4 d FIG. 4, electrical structure 4 e of FIG. 5 comprises a plurality of FETs 17 d . . . 17 k. FET 17 d comprises a source 6 a, a drain 7 a, and a gate structure 16 c. FET 17 e comprises a source structure 8 a, drain structure 7 a (i.e., a shared drain structure), and gate structure 16 c. FET 17 f comprises a source structure 6 b, a drain structure 7 b, and gate structure 16 c. FET 17 g comprises a source structure 8 b, drain structure 7 b (i.e., a shared drain structure), and gate structure 16 c. FET 17 h comprises a source structure 6 c, a drain structure 7 c, and gate structure 16 c. FET 17 i comprises a source structure 8 c, drain structure 7 c (i.e., a shared drain structure), and gate structure 16 c. FET 17 k comprises a source structure 6 d, a drain structure 7 d, and gate structure 16 c. FET 17 j comprises a source structure 8 d, drain structure 7 d (i.e., a shared drain structure), and gate structure 16 c. Electrical structure 4 e comprises a deep trench 21 c forming a perimeter surrounding FETs 17 d . . . 17 k. Additionally, deep trench 21 c comprises portions formed between:

1. FETS 17 d and 17 e and FETS 17 f and 17 g. 2. FETS 17 f and 17 g and FETS 17 h and 17 i. 3. FETS 17 h and 17 i and FETS 17 k and 17 j.

A gate dielectric (e.g., oxide) liner 16 c is formed within (i.e., lining) deep trench 21 c and a gate structure 14 c is formed over gate dielectric liner 16 c and within trench 21 c. Deep trench 21 c, gate dielectric (e.g., oxide) liner 16 c, and gate structure 14 c in combination form a perimeter structure that surrounds FETs 17 d . . . 17 k. Additionally, deep trench 21 c, gate dielectric (e.g., oxide) liner 16 c, and gate structure 14 c in combination form an isolation structure that separates:

1. FETS 17 d and 17 e from FETS 17 f and 17 g. 2. FETS 17 f and 17 g from FETS 17 h and 17 i. 3. FETS 17 h and 17 i from FETS 17 k and 17 j.

The structure formed by deep trench 21 c, gate dielectric (e.g., oxide) liner 16 c, and gate structure 14 c isolates (i.e., electrically and mechanically):

1. FETS 17 d and 17 e from FETS 17 f and 17 g. 2. FETS 17 f and 17 g from FETS 17 h and 17 i. 3. FETS 17 h and 17 i from FETS 17 k and 17 j.

Additionally, the structure formed by deep trench 21 c, gate dielectric (e.g., oxide) liner 16 c, and gate structure 14 c isolates (i.e., electrically and mechanically) FETS 17 d . . . 17 k a from additional components (e.g., FETS, resistors, capacitors, wires, etc) that are located on electrical structure 4 e. Gate dielectric (e.g., oxide) liner 16 c may comprise a thickness of about 3000 A.

FIG. 6A depicts a third alternative to FIG. 1A illustrating a top view of an electrical structure 4 f, in accordance with embodiments of the present invention. In contrast with electrical structure 4 a FIG. 1A, electrical structure 4 f of FIG. 6A comprises a field effect transistor (FET) 171 formed on a P substrate 24. FET 171 comprises an N+ source structure 11 formed over an N-tub 18 c and an N+ drain structure 9 formed over a N-tub 18 d.

FIG. 6B illustrates a cross sectional view of electrical structure 4 a of FIG. 6A, in accordance with embodiments of the present invention. The cross sectional view of FIG. 6B is taken along line 6B-6B of FIG. 6A.

FIG. 7A depicts a first alternative to FIG. 6A illustrating a top view of an electrical structure 4 g, in accordance with embodiments of the present invention. In contrast with electrical structure 4 f FIG. 6A, electrical structure 4 g of FIG. 7A comprises an FET 17 j that comprises an N-well 25 c formed between N-tub 18 c and source structure 11 and an N-well 25 d formed between N-tub 18 d and drain structure 7. An N-well is defined herein as a moderately N doped CMOS device.

FIG. 7B illustrates a cross sectional view of electrical structure 4 g of FIG. 7A, in accordance with embodiments of the present invention. The cross sectional view of FIG. 7B is taken along line 7B-7B of FIG. 7A.

FIG. 8A depicts a combination FIGS. 2A and 3A illustrating a top view of an electrical structure 4 h, in accordance with embodiments of the present invention. FIG. 8A comprises the P-wells 25 a and 25 b of FIG. 2A added to FET 17 a of FIG. 3A. In contrast with electrical structure FIGS. 2A and 3A, electrical structure 4 h of FIG. 8A comprises a gate contact 12 a in an alternative location.

FIG. 8B illustrates a cross sectional view of electrical structure 4 h of FIG. 8A, in accordance with embodiments of the present invention. The cross sectional view of FIG. 8B is taken along line 8B-8B of FIG. 8A.

FIGS. 9A-4H illustrate a process for generating electrical structure 4 h of FIGS. 8A and 8B, in accordance with embodiments of the present invention.

FIG. 9A illustrates a cross sectional view of a P type substrate 24, in accordance with embodiments of the present invention.

FIG. 9B illustrates a cross sectional view of an N-tub layer 22 formed from P type substrate 24, in accordance with embodiments of the present invention. N-tub layer 22 may be implanted and annealed to diffuse.

FIG. 9C illustrates a cross sectional view of P tub implants 18 a and 18 b formed from N-tub layer 22, in accordance with embodiments of the present invention. P tub implants 18 a and 18 b may be implanted and annealed to diffuse.

FIG. 9D illustrates a cross sectional view of gate structure 12 a formed in deep trench 21 a, in accordance with embodiments of the present invention. Deep trench 21 a is etched to comprise a width of about 1 um and a depth of about 6 um. Gate dielectric (e.g., oxide) liner 16 a is formed in deep trench 21 a and gate structure 14 a is formed over gate dielectric liner 16 a.

FIG. 9E illustrates a cross sectional view of shallow trench isolation structure 20 formed over N-tub layer 22, in accordance with embodiments of the present invention.

FIG. 9F illustrates a cross sectional view of P wells 25 a and 25 b formed in P tubs 18 a and 18 b, in accordance with embodiments of the present invention.

FIG. 9G illustrates a cross sectional view of FIG. 9F after gate contact 12 a has been formed, in accordance with embodiments of the present invention.

FIG. 9H illustrates a cross sectional view of FIG. 9G after source structure 6 and drain structure 7 have been formed, in accordance with embodiments of the present invention.

While embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention. 

1. An electrical structure comprising: a semiconductor substrate comprising a deep trench; an oxide liner layer formed over an exterior surface of said deep trench; and a first field effect transistor (FET) formed within said semiconductor substrate, wherein said first FET comprises a first source structure, a first drain structure, and a first gate structure, wherein said first gate structure comprises a first gate contact connected to a first polysilicon fill structure, wherein said first polysilicon fill structure is formed over said oxide liner layer and within said deep trench, wherein said first polysilicon fill structure is configured to flow current laterally across said first polysilicon fill structure such that said current will flow parallel to a top surface of said semiconductor substrate.
 2. The electrical structure of claim 1, wherein said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination form a first perimeter that circumscribes said first source structure and said first drain structure.
 3. The electrical structure of claim 2, further comprising: a second FET formed within said semiconductor substrate, wherein said second FET comprises a second source structure, a second drain structure, and said first gate structure, wherein said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination form a second perimeter that circumscribes said second source structure and said second drain structure, and wherein a first portion of said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination isolates said first source structure and said first drain structure from said second source structure and said second drain structure.
 4. The electrical structure of claim 2, further comprising: a second FET formed within said semiconductor substrate, wherein said second FET comprises a second source structure, said first drain structure, and said first gate structure, wherein said first perimeter circumscribes said second source structure.
 5. The electrical structure of claim 4, further comprising: a third FET formed within said semiconductor substrate, wherein said third FET comprises a third source structure, a second drain structure, and said first gate structure; and a fourth FET formed within said semiconductor substrate, wherein said fourth FET comprises a fourth source structure, said second drain structure, and said first gate structure, wherein said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination form a second perimeter that circumscribes said third source structure, said fourth source structure, and said second drain structure, and wherein a second portion of said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination isolates said first source structure, said second source structure, and said first drain structure from said third source structure, said fourth source structure, and said second drain structure.
 6. The electrical structure of claim 1, wherein said first source structure comprises a first P tub formed within said semiconductor substrate, a first P well formed within said first P tub, and a first P+ region formed over said first P well, and wherein said wherein said first drain structure comprises a second P tub formed within said semiconductor substrate, a second P well formed within said second P tub, and a second P+ region formed over said second P well.
 7. The electrical structure of claim 1, wherein said semiconductor substrate comprises a P layer and an N tub layer formed over said P substrate, wherein a portion of said deep trench structure extends into said N tub layer.
 8. The electrical structure of claim 1, wherein said first source structure comprises a first N tub formed within said semiconductor substrate, a first N well formed within said first N tub, and a first N+ region formed over said first N well, and wherein said first drain structure comprises a second N tub formed within said semiconductor substrate, a second N well formed within said second N tub, and a second N+ region formed over said second N well.
 9. The electrical structure of claim 1, wherein said first gate structure comprises a plurality of gate contacts connected to said first polysilicon fill structure.
 10. The electrical structure of claim 1, wherein said first FET comprises a high voltage FET configured to operate at voltages selected from a range of about 10 volts to about 200 volts.
 11. A method for forming an electrical structure comprising: providing a semiconductor substrate; forming a deep trench structure within said semiconductor substrate; forming an oxide liner layer over an exterior surface of said deep trench; and forming a first field effect transistor (FET) within said semiconductor substrate, wherein said first FET comprises a first source structure, a first drain structure, and a first gate structure, wherein said first gate structure comprises a first gate contact connected to a first polysilicon fill structure, wherein said first polysilicon fill structure is formed over said oxide liner layer and within said deep trench, wherein said first polysilicon fill structure is configured to flow current laterally across said first polysilicon fill structure such that said current will flow parallel to a top surface of said semiconductor substrate.
 12. The method of claim 11, wherein said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination form a first perimeter that circumscribes said first source structure and said first drain structure.
 13. The method of claim 12, further comprising: forming a second FET within said semiconductor substrate, wherein said second FET comprises a second source structure, a second drain structure, and said first gate structure, wherein said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination form a second perimeter that circumscribes said second source structure and said second drain structure, and wherein a first portion of said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination isolates said first source structure and said first drain structure from said second source structure and said second drain structure.
 14. The method of claim 12, further comprising: forming a second FET within said semiconductor substrate, wherein said second FET comprises a second source structure, said first drain structure, and said first gate structure, wherein said first perimeter circumscribes said second source structure.
 15. The method of claim 14, further comprising: forming a third FET within said semiconductor substrate, wherein said third FET comprises a third source structure, a second drain structure, and said first gate structure; and forming a fourth FET within said semiconductor substrate, wherein said fourth FET comprises a fourth source structure, said second drain structure, and said first gate structure, wherein said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination form a second perimeter that circumscribes said third source structure, said fourth source structure, and said second drain structure, and wherein a second portion of said deep trench, said oxide liner layer, and said first polysilicon fill structure in combination isolates said first source structure, said second source structure, and said first drain structure from said third source structure, said fourth source structure, and said second drain structure.
 16. The method of claim 11, wherein said first source structure comprises a first P tub formed within said semiconductor substrate, a first P well formed within said first P tub, and a first P+ region formed over said first P well, and wherein said wherein said first drain structure comprises a second P tub formed within said semiconductor substrate, a second P well formed within said second P tub, and a second P+ region formed over said second P well.
 17. The method of claim 11, wherein said semiconductor substrate comprises a P layer and an N tub layer formed over said P substrate, wherein a portion of said deep trench structure extends into said N tub layer.
 18. The method of claim 11, wherein said first source structure comprises a first N tub formed within said semiconductor substrate, a first N well formed within said first N tub, and a first N+ region formed over said first N well, and wherein said first drain structure comprises a second N tub formed within said semiconductor substrate, a second N well formed within said second N tub, and a second N+ region formed over said second N well.
 19. The method of claim 11, wherein said first gate structure comprises a plurality of gate contacts connected to said first polysilicon fill structure.
 20. The method of claim 11, wherein said first FET comprises a high voltage FET configured to operate at voltages selected from a range of about 10 volts to about 200 volts. 